It is hard to tell what you are going to need in SHTF in your medical part of prepping. Easiest thing to say is that you gonna need everything, but actually it depends from your level of medical knowledge i guess.
for example:

List is going more, but important is to choose what level you want to know, then find way to learn to use things on that level. You can not know everything. Maybe you gonna choose only to have powdered things for hydration instead of IV NS.

Whatever you choose to have, keep in mind that must be as more disposable as you can. For example paper instead of fabric, or sterile plastic tweezers instead of reusable. And again from my experience most of the problems were coming in the form of vomiting and diarrhea, due to bad water, or unknown food.

Hello and welcome
If we are talking about medical or any other thing, if you have enough money buy everything disposable. It is easy to say disinfect it between uses, you can disinfect some things but most of the equipment you gonna need to make sterile and keep sterile again, that s different thing.
You not gonna have (probably) electric power, running water, if you are very good prepared you gonna be able to keep your self clean, barely, but to keep your equipment (medical) sterile in SHTF condition and make it ready for multiple use it is gonna be very hard, not to mention that you gonna have more important things on your mind. If you can not keep your equipment in perfect condition you have increasing risk of infection, that brings whole new problem in already problematic situation.

Of course same is with plastic cups, paper plates, paper towels, diapers. You not gonna be able to clean everything after use. Infections will spread, that s for sure. Can you imagine how many problems brings simple case of diarrhea in that situations?
Keep it disposable as more and as long as you can.
Disposable things will solve one of your problems in SHTF situation.
Thanks
Selco

Very good point on the difficulty of sterility without supporting infrastructure.
The only concern I would have would be the volumes of disposables needed.
I currently stock some of the disposable kits (wound dressing/debridement,suture etc) and these would be the first used . What would you consider the most useful? (child birth,suture,dressing,?)

As more as you can,depends on your budget , space and skills.
i found medical skills and preparations like some of mine most important preparing, so i have it a LOT.
But that s me, i am also in normal time in medical field.
I would say that you gonna need probably more things to care for wounds and cuts then to care about childbirth.
Also you can easily setup child birth set from your sterile equipment, like sterile tweezers,forceps-clamps, gowns, sterile gloves and pads, sterile suction bulbs,small BVM etc.

Thank you and welcome
Some of the hospitals in other areas in that time used similar kind of sterilization with hand made sterilizers.
About pressure cookers, some folks also made kind of portable stoves from them.

Unless you are trained in proper/appropriate use and dosage, consider them trade items, or as stock for your group medic. Study up on storage needs and real shelf lives. The US military has recent research material available on the web.

In SHTF and lack of available resources, desperate times make people do desperate things. The problem comes when someone does something and does not know what they are doing.
If you are an EMT-P, RN, PA, MD thats a good start. Now go and take some trauma courses and austere
medicine training. After that start stocking up on supplies for the most frequent injury/illness.
Without that background, I don’t recommend you try to treat any serious illness/injury.
I do recommend you find one of the above mentioned people and make them part of your prep group.
Many non-medical US military personnel have been trained in treating combat trauma, and that is paying dividends on the battlefield, but they know nothing about treating a case of appendicitis or pneumonia.
Do you really want it on your conscious that your child died because you thought you were treating a simple asthma flare and they actually were having RADS?

It’s pointless to try to conduct medical procedures that are over your head and above your level of training.

For people who haven’t been trained in depth on complex medical procedures, do not complicate things by attempting something that you have no knowledge of.

Learn what you can, stock what you know how to use in your FAK/Trauma kit. Sometimes there are alternatives that can be used. For example, if you are not trained/practice on suturing, super glue works well to close up wounds.